1. Field of the Invention
The invention relates to a management system for the operation of a wind turbine, which regulates the power output of the turbine.
2. Description of Related Art
Generic management systems are used in wind turbines comprising a rotor with at least one rotor blade, wherein the rotor blade is positioned at an adjustable angle to the rotor. The management system regulates the rotor speed within a predefined wind speed range by varying the rotor blade angle in order to set a nominal output.
If a wind turbine is operated while wind speeds are too high, the turbine may be destroyed by the high mechanical load. For that reason, generic management systems are designed such that they turn off the turbine in excess of a defined turn-off wind speed, wherein the turbine is preferably not turned off in an abrupt manner, but by slowly reducing the output. For example, a generic management system is disclosed in DE 195 32 409 A1.
DE 198 44 258 A1 also discloses a management system which is used to reduce the output as soon as the wind speed reaches a predefined value. Herein, reduction in output is also achieved by varying the rotor blade angle. However, reduction in output is already initiated when a wind speed threshold value is reached, wherein the wind speed threshold value is lower than the turn-off wind speed.
The reduction in output is intended to reduce the mechanical load exerted on the turbine, wherein said mechanical load rises with increasing wind speed; thereby, the turbine can be designed with less powerful dimensions, thus also permitting lowering of costs.
Both of the management systems described above start to reduce the output as soon as a defined wind-speed-dependent threshold value is reached. Said threshold value is based on the wind speed measured. Usually, the wind speed is measured by means of a nacelle anemometer. This measurement method is relatively inaccurate and, thus, fails to provide a good indicator of the load exerted on the turbine.
For that reason, the threshold value in excess of which the management system reduces the output a wind turbine should not be based on the wind speed measured but on an input variable that can be determined more easily, both physically and with regard to the controller used.